1. Field of the Invention
The present invention relates to an apparatus for non-invasive, real-time, accurate, continuous monitoring of hemoglobin concentration and hematocrit and a method for continuously or discretely monitoring hemoglobin concentration and hematocrit.
More particularly, the present invention relates to an optoacoustic apparatus including a nanosecond pulsed-laser, a fiber-optic delivery system and a probe including a sensitive acoustic transducer and hardware and software for converting a received acoustic signal into a measurement of hemoglobin concentration and hematocrit and to methods for monitoring hemoglobin concentration and hematocrit using the apparatus and methods for making the apparatus.
2. Description of the Related Art
Continuous noninvasive monitoring of blood hemoglobin concentration and hematocrit offers great promise in the diagnosis and management of many diseases and life-threatening conditions, such as emergency department stabilization of hemorrhaging patients, management of critically ill patients in Intensive Care Units, and performance of extensive surgical procedures. Current techniques are invasive, requiring blood sampling and analysis, and cannot be performed continuously, in real time for extended intervals. Presently, there is no system for accurate, non-invasive, and continuous monitoring of hemoglobin concentration and hematocrit.
Because of the importance of hemoglobin concentration in oxygen delivery, hematocrit and hemoglobin are among the most frequently obtained blood tests in both outpatients and inpatients. Current techniques for measuring hemoglobin concentration and hematocrit require withdrawal of a blood sample from a vein or artery. Subsequently, the sample can be centrifuged, separating the fraction of red cells from plasma or chemically analyzed. These techniques are accurate but invasive and can result in iatrogenic anemia in patients who require frequent blood sampling [3-7]. Continuous invasive techniques are available for monitoring hemoglobin concentration, but these require access to an extracorporeal loop containing circulating blood (as is present, for example, during hemodialysis) [8-12]. Although noninvasive techniques such as pulse oximetry are available to monitor arterial oxygen saturation, no noninvasive technique is available to monitor hemoglobin concentration or hematocrit.
One additional major problem with intermittent measurement of hemoglobin concentration or hematocrit is the inevitable delay associated with withdrawal of a blood sample, transport to a measuring device, and processing. If the laboratory is remote from the site of care, the delay can be considerable. Even if the laboratory is in close proximity to the site of care, frequent sampling in a critically ill patient may occupy a substantial proportion of a technician""s time, thereby increasing the cost of care and limiting the availability of that technician for other duties.
Thus, there is a need in the art for a non-invasive, real-time, accurate, continuous apparatus and a method using the apparatus for monitoring hemoglobin concentration and hematocrit.
The present invention provides an optoacoustic apparatus including a nanosecond pulsed laser and a fiber-optic delivery system including a plurality of optical fibers, where the system is connected to an output of the laser at its proximal end. The apparatus also includes a probe including a piezoelectric transducer mounted in a front face of the probe and a back portion adapted to receive the fiber-optic delivery system. The optical fibers terminate at the front face of the probe and are distributed around or surround the transducer. The transducer is connected via a cable which exits out of the back of the probe to a processing unit that converts the transducer output into a continuous measure of hemoglobin concentration and hematocrit.
The present invention also provides an optoacoustic apparatus for monitoring hemoglobin concentration in the aorta of an animal comprising a pulsed radiation source; an optical system including an optical fiber, an optical screen and an acoustic screen, where the system is connected to an output of the radiation source at its proximal end; a probe including a housing, a tip, a ring-shaped piezoelectric element, a backing element and an isolating layer, where the optical system enters the housing at its proximal end passes through a center of the piezoelectric element and terminates flush with the housing at the probers tip; a cable connected to the transducer at its proximal end and exiting the probe out of the proximal end of the probe; and a processing unit connected to the distal end of the cable for converting the transducer output into a measure of aorta hemoglobin concentration and/or hematocrit.
The present invention also provides a probe including a front face having mounted thereon a piezoelectric transducer connected to an output cable that exits a back portion of the probe, a plurality of optical fibers entering the probe from the back portion of the probe and terminating at or in the front face of the probe, where light from a laser is sent through the fibers and exit the probe at its front face causing an acoustic response which is measured by the transducer mount in the probe.
The present invention further provides a method for continuously measuring optoacoustic monitoring of hemoglobin concentration and hematocrit including the step of directing radiation pulse from a laser via optical fibers into a probe of present invention having its front face in contact with a tissue site (blood vessel) of an animal including human. The light pulse leaves the probe face and enters the tissue site causing the production of an acoustic signal. The acoustic signal is received by a transducer mounted on the front face of the probe. The signal is then transmitted to a processing unit which converts the signal into a measure of hemoglobin concentration and hematocrit. The method can also include displaying the measurement on a display device. Preferably, the radiation is pulsed and particularly, the radiation is pulsed in a nanosecond time frame.
The present invention also provides a system for carrying out the above-stated method including a pulsed laser system or other system capable of generating short optical pulses to provide irradiation of a tissue or vessel. The systems also includes a light communication system such as a fiber-optic system or articulated mirror arm optical system for delivering laser pulses to the tissue or vessel and an acoustic detection systems including at least one acoustic transducer for pressure profile detection with sufficient sensitivity, temporal resolution, and bandwidth so that thermoelastic optoacoustic pressure profiles of the absorbed laser energy in the tissue or vessel can be detected. The system also includes an adjustable holder for the light delivery system and the acoustic transducer(s) to provide appropriate irradiation conditions and acoustic contact between the investigated tissue or vessel and the acoustic transducer(s) and an electronic system for signal recording and processing. The system can also include a digital processing or computer system that converts a signal from the acoustic detection system into a measure the hemoglobin concentration of blood in a tissue or vessel.
The present invention still further provides a method for relating an acoustic signal to an hemoglobin concentration of arterial or venous blood in a tissue site of an animal including a human.